As a power supply which drives an industrial motor or server, one which includes first and second semiconductor switching elements connected in series to form a half bridge circuit, and which supplies power to a load, such as the motor, from the midpoint of the half bridge circuit, is known. The first and second semiconductor switching elements of this kind of power supply are each formed of, for example, an IGBT or a high voltage power MOS-FET. In particular, the first semiconductor switching element on the high potential side is driven on/off with a first voltage, which is a midpoint potential of the half bridge circuit, as a reference potential. Also, the second semiconductor switching element is driven on/off with a second voltage lower than the first voltage, specifically, a ground potential as a reference potential. Further, complementarily driven on/off, the first and second semiconductor switching elements switch a predetermined voltage applied to the half bridge circuit and supply the power to the load.
Herein, the complementary on/off drive of the first and second semiconductor switching elements is carried out, in general, using a semiconductor device forming a high voltage compatible integrated circuit which is referred to as a so-called HVIC (High Voltage Integrated Circuit). This kind of semiconductor device includes, for example, a first circuit, which operates with the first voltage as the reference potential, as the high side circuit, and a second circuit, which operates with the second voltage different from the first voltage as the reference potential, as the low side circuit. Specifically, the first circuit configures a first driver which drives on/off the first semiconductor switching element. Also, the second circuit configures a second driver which drives on/off the second semiconductor switching element.
The semiconductor device, upon receiving in the low side circuit a low potential control signal given from a controller, such as a microcomputer, which dominates the control of the whole of a system, transmits the control signal to the first and second drivers, thereby controlling the operation of the semiconductor device. Specifically, the semiconductor device drives the second driver in accordance with the control signal, and drives the first driver by level shifting the control signal, specifically, stepping up the control signal to a high potential, and transmitting the high potential control signal to the high side circuit.
Meanwhile, the semiconductor device includes in each of the high side circuit and low side circuit an anomaly detection circuit which detects abnormal heat generation, overcurrent, or the like of the first and second semiconductor switching elements. The semiconductor device level shifts an anomaly signal, such as abnormal heat generation or overcurrent, which is detected in the high side circuit, specifically, steps down the anomaly signal to a low potential, and transmits the low potential anomaly signal to the low side circuit. Further, a control circuit provided in the low side circuit stop controls the operation of the semiconductor device by stopping the transmission of the control signal to the first and second drivers when an anomaly signal, such as the abnormal heat generation or overcurrent, is detected. Also, an alarm output circuit provided in the low side circuit outputs an alarm signal when an anomaly, such as the abnormal heat generation or overcurrent, is detected, and notifies the controller, such as a microcomputer. The controller, when receiving the alarm signal, changes the control of the semiconductor device or stops the drive of the semiconductor device and thereby protects the whole of the system.
In the meantime, when the first semiconductor switching element on the high potential side of the half bridge circuit operates off, it sometimes happens that a negative voltage surge is applied to the semiconductor device due to inductance included in a load such as the motor. The negative voltage surge is the phenomenon that the reference potential of the half bridge circuit defined by the midpoint potential of the half bridge circuit instantaneously becomes lower than the ground potential which is the reference potential of the low side circuit. Then, a large current flows into the semiconductor device from a ground potential terminal due to the negative voltage surge, and there is fear that the semiconductor device breaks down due to the large current.
In order to prevent this kind of breakdown of the semiconductor device due to the negative voltage surge, it is disclosed in, for example, PTL 1 that a diode is provided in inverse parallel between a midpoint potential terminal which defines the first voltage in the semiconductor device and the ground potential terminal which sets the second voltage, and that the potential of the negative voltage surge is clamped by the diode. Also, it is disclosed in PTL 2 to improve the structure of a device itself configuring the semiconductor device, thereby enhancing the surge breakdown voltage of the semiconductor device and protecting the semiconductor device. Furthermore, it is disclosed in PTL 3 that the current flowing into the semiconductor device from the ground potential terminal is suppressed by a resistance element, thereby limiting the current when the negative voltage surge occurs and protecting the semiconductor device.